1. Field of the Invention
The present invention relates to priority switching apparatuses of an input signal. More particularly, the present invention relates to a priority switching apparatus of an input signal that can automatically switch among input signals applied to respective input terminals in a monitor display device including a plurality of input terminals.
2. Description of the Background Art
The spread of personal computers in these days is remarkable. The color display monitors connected to these personal computers are provided with various functions. One such function is an input switching function. BNC connectors and a Dsub connector are provided at the back side of the display. Input signals that are applied to these connectors can be switched by a switch that is provided at the front side of the display. A BNC connector is connected individually to a coaxial cable for each video signal of R, G, and B, and to horizontal and vertical synchronizing signals respectively. The Dsub connector includes a plurality of pins. The coaxial cable of each video signal of R, G, and B and horizontal and vertical synchronizing signals is connected to the pins of the Dsub connector. A system is proposed in Japanese Laid-Open Patent No. 6-51729 wherein an input signal path with a synchronizing signal is automatically detected and switched to even when a plurality of input terminals are connected.
A display employing such a method can be installed in dealing rooms of banks and securities companies. The display may be used as a monitor of a word processor, and switched, if necessary, to display stock information, for example. However, a limitation exists in that the switch of the display must be effected every time to confirm whether stock information is displayed or not. In other words, a change in the signal that is not displayed cannot be identified in real time. Information cannot be obtained instantaneously when used in dealing systems and the like.
In order to automatically switch the input of the display when stock information, for example, is input as input signals, the switching circuit disclosed in the aforementioned Japanese Laid-Open Patent No. 6-51729 detects the frequency of a synchronizing signal of an input signal of another terminal when the currently selected input terminal does not have a synchronizing signal, and the input signal path is automatically switched. However, the path cannot be switched to another input signal path if a synchronizing signal is applied to the selected input terminal.